Sprinkler devices are well known and well accepted devices for protection of homes, offices, factories, and the like, against fire.
Conventional sprinkler devices typically utilize a heat-sensitive element which may, for example, melt at a predetermined temperature enabling a spring-loaded valve to open and spray water upon a predetermined area protected by the sprinkler device. Such devices have the disadvantage of remaining open and being incapable of reclosing due to destruction of the meltable element.
The need as well as the desire to provide sprinkler devices with an on-off capability have led to the development of sprinkler devices which have the capability of opening responsive to an emergency condition and reclosing when the emergency condition terminates. Note, for example, U.S. Pat. No. 3,757,866 which has a pilot valve actuated by a bimetal disk which normally biases the pilot valve to a closed condition, sealing a control opening communicating between a chamber in which a piston is reciprocatingly mounted and an outlet opening. Water enters through an inlet opening and passes through a restricted opening in the center of the piston to fill the aforementioned closed chamber whereby equal water pressure is applied on opposite surfaces of the piston but with the larger surface area of the piston confronting the closed chamber, the piston is urged to the closed position, sealing a second opening communicating between said inlet and said outlet.
The bimetal opens the valve to unseal the control opening when ambient temperature reaches a predetermined level such as 185.degree. F. allowing water in the previously closed chamber to pass through the outlet opening abruptly dropping the pressure applied to the bottom surface of the piston enabling the piston to be moved to a position unsealing the opening between the inlet and outlet.
The valve reseals the control opening between the chamber and the outlet opening responsive to a reduced ambient temperature, typically of the order of 100.degree. F., whereupon the chamber is refilled causing the liquid pressure build-up within the chamber to move the piston back to the position resealing the opening communicating the inlet with the outlet.
The above system, which is described in detail, for example, in U.S. Pat. No. 3,757,866, has a disadvantage of requiring O-ring sealing devices to prevent liquid filling the chamber from reaching the outlet opening, thus increasing the forces required to move the piston to both the sealed and the unsealed positions. The O-rings increase the force needed to move the piston. In addition, the useful operating life of the O-rings is limited, necessitating frequent maintenance and repair. For example, the average shelf life of an O-ring is of the order of fifteen years whereas the average life of a sprinkler device is of the order of fifty years. In addition, the shape of the piston necessitates the provision of two sliding chambers of different diameter for slidably mounting the piston.
Other sprinkler devices having on-off capabilities similar in design to the above-mentioned patent include: U.S. Pat. Nos. 3,698,483; 3,791,450; 3,802,510; 3,848,676; 4,553,602; 4,706,758; 4,830,117 and 4,830,118. The devices of all the above-mentioned patents have the disadvantage of requiring O-ring seals, as well as independent biasing members.
U.S. Pat. No. 4,359,098, in addition to requiring O-ring seals and biasing members, further requires a flexible diaphragm which is subject to wearing and deterioration at a rate equal to or greater than that experienced by the O-rings.